This chapter describes methods used in seedling-rearing
stations for culturing young sporelings. Zoospores are collected
on substrates (either palm coir “sporeling ropes” or bamboo rod
“chopsticks”) where they develop into gametophytes. Male and
female gametes produced by gametophytes combine sexually to form
zygotes which develop into sporelings. The gametophyte generation
is completed in about twelve days. Sporelings attached to
sporeling ropes are cultured in the seedling station for a period
of three months. After reaching a length of 2–5 cm the sporeling
ropes are transferred to the raft site for intermediate culture

Since the early 1950's two basic methods have been used for
Laminaria sporeling culture: (i) outdoor sporeling culture under
natural conditions in seawater, used between 1949–1956, and (ii)
indoor sporeling culture under artificially controlled conditions
in a seedling-rearing station, used after 1956. The artificial
seedling-rearing method of sporeling culture may also be subdivided
into two methods: (a) seedling-rearing with an artificial
light source (fluorescent lamps), used between 1956–1958, and (b)
seedling-rearing with natural daylight (a glass house), developed
after 1958.

Natural Sporeling Culture in Seawater

In the early 1950's sporeling culture was done outdoors in
shallow sea regions. Spores were collected in mid-October, when
seawater temperature drops to 20° C, by lowering bamboo substrates
into parent Laminaria beds. The bamboo substrates, flat
bamboo sections about 0.5 m in length and 10 cm in width, were
tied together in series like rope ladders (Fig. 3.1). They were
anchored in place and buoyed with glass floats. Zoospores
released into seawaters by parent kelp plants attached to the
bamboo substrates and developed into “autumn sporelings”. After
about three months of growth the young sporelings were transplanted
to thicker culture ropes which were suspended from
floating raft ropes for the final grow-out period.

Artificial Sporeling Culture in Seedling Stations

After 1956 a new “summer sporeling” culture method was
developed to overcome many of the problems encountered with
“autumn sporeling” culture. Under this new method, now widely
practiced in China, zoospores are collected in mid-July before
seawater temperatures rise above 20° C and are cultured indoors
in seedling stations using artificially cooled seawater. The
zoospores are induced to adhere to artificial substrates such as
bamboo rods or palm-fibre seedling cords. The substrates are
submerged in culture tanks through which cooled water is
circulated. Water temperature is maintained at between 8–12°C,
preferably 8–10°C, throughout the seedling-rearing process.
After three months of growth in the seedling station (mid-July to
mid-October) young sporelings reach a length of between 2–5 cm.

In mid-October when seawater temperature falls to about 20°
C the summer sporelings grown to a length of 2–5 cm in seedling
stations are transferred to raft ropes in natural seawaters.
Following an intermediate culture period of 2–4 weeks (mid-October
to mid-November), during which sporelings grow in length
to between 10–25 cm, young sporophyte plants are ready to be
transplanted from the sporeling ropes to thicker culture ropes
which are suspended from floating raft ropes for the final growout
period. The grow-out period lasts until harvest in mid-July
of the following year.

As discussed in Chapter I, the use of artificial seedling-rearing
techniques for growing summer sporelings lengthens the
growing season by 2–3 months and increases yield by 40%, compared
with methods previously used for culturing autumn sporelings.

Artificial Seedling-rearing Using Natural Daylight

Seedling stations constructed in the mid-1950's were closed
buildings in which lighting was provided by fluorescent lamps. In
the late 1950's “glass house” seedling stations were constructed
so that natural daylight could be used instead of fluorescent
lamps, thus saving on electricity costs. The refinement is
sometimes referred to as “industrial sporeling culture under
daylight”. As in agricultural greenhouses, illumination is
controlled in the seedling-rearing “glass houses” with curtains
that can be opened or closed depending on light exposure
required. As before, seawater is artificially cooled to stimulate
the growth of young sporelings.

The first seedling station designed to use natural daylight
was built in Shandong Province in 1958. Its glass-enclosed
culture room had a total area of 5,200 m with a production
capacity of 400 million sporelings per year, highest in the world
for such a facility. Today the new design has become an industry-wide
standard.

The seedling-rearing station is composed of two main
systems: (i) the sporeling culture room, and (ii) the water
circulation system. The former system includes the glass house
and culture tanks used for controlling illumination and for
sporeling culture. The latter system includes: (a) the filtration
system for purifying seawater, (b) the indoor water circulation
system for pumping seawater through the culture tanks.

Site Selection for the Seedling Station

Successful sporeling culture depends on such factors as
seawater quality, daylight exposure and building design. Site
selection must consider these and other factors which determine
operational efficiency. The following are important criteria for
site selection:

The station should be located on the shore near
seawater so that pumping costs are reduced to a
minimum.

The station should be located far away from any
sources of water pollution, such as harbours,
estuaries, industrial or residential areas.

The station should be located at a place where
the nearshore seafloor is sandy or rocky so that
pumped seawater will not contain excessive amounts
of mud or organic debris.

The station should be located in open terrain
where there are no trees or high buildings to block
sunlight or impede air circulation.

The station should be located on a level site
where ground is firm, avoiding sandy beaches and
regions with soft soils, in order to provide a
solid foundation for the building structures.

The station should be located at a place where
there are good utilities and transportation
services, i.e. where there are good roads, a good
power supply and a good supply of freshwater.

General Layout of the Seedling Station

The design of the main building structure must be economical
and must suit particular conditions found at the building site.
The sporeling culture room containing the culture tanks, as well
as the other associated structures (a pumping station, water
filtration tank), must be built on firm and level ground. Piping
systems should be buried underground.

Layout of the Sporeling Culture Room

The sporeling culture room, or “glass house”, is the main
structure of the seedling station, where the culture tanks are
placed for raising sporelings. The typical sporeling culture
room, designed for production of 400 million sporelings annually,
is constructed like a greenhouse. The interior area of the
culture room, usually about 5,200 m2, is enclosed with a glass-pane
roof. All open spaces of the culture room should be equally
exposed to bright daylight, with no supporting walls or other
shadow-making fixtures blocking incoming light.

The four outer walls of the “glass house” or “culture room”
should be made of reinforced concrete rising about 60 cm above
ground level. The inner floor area of the culture room, made of
poured reinforced concrete, should be designed so that there is a
gradient of levels, like a series of steps, each floor level
designed to hold a row of culture tanks (Fig. 3.2). The glass
roof of the station should be positioned to face east-west in
order to receive highest daylight exposure. Glass roof sections
imbedded in a metal frame are raised over the culture room.
Glass walls are constructed between the cement foundation and the
glass roof structure. The roof may be formed of one or two
layers of glass depending on the degree of insulation required
for maintaining stable indoor temperature.

Simple but effective systems must be installed for adjusting
air circulation and light intensity. Indoor window shutters
should be built along the glass walls. Moveable curtains should
be fixed in place below the glass roof. Light intensity may be
further controlled by painting the exterior surfaces of the glass
roof with light-reflecting white paint. Methods for adjusting
air circulation are required, such as hinged windows in the glass
walls and circulation fans.

Building materials should be strong, durable and noncorrosive.
In China, construction teams often use prefabricated
reinforced concrete components that can be welded in place,
especially for framing main structural elements such as roof
beams, supporting pylons and window frames. Materials such as
wood and iron which decay or corrode quickly when exposed to
seawater or high humidity should be avoided as much as possible.

Fig. 3.2. Layout of seedling station culture room.

Showing the glass-roofed culture room with culture tanks
arranged on different floor levels to enable a gravity-fed
water circulation system.

If the culture room is built on sandy subsoil a reinforced
concrete retaining wall should be constructed around its outer
periphery to prevent shifting of the subsoil. Highly reinforced
concrete should be used in floor areas that will support the
weight of culture tanks to prevent cracks and seepage of
seawater.

Culture tanks are made of reinforced cement, their
dimensions depending on their arrangement in the culture room.
Culture tanks are usually about 8–10 m in length, 2.15–2.3 m in
width and 0.3 m in height. The tanks should be designed so that
they fit in rows on the gradient of floor levels in the culture
room. This system allows deployment of a gravity-fed water
circulation system, enabling seawater to flow from one row of
tanks placed on an upper level of the culture room to another row
of tanks placed on a lower level (Fig. 3.2).

If there are six or fewer levels across the open floor area
of the culture room and if 20% of total seawater in the water
supply system is changed daily, the water temperature differential
between entry and exit canals of the culture room should
be less than 2° C.

Layout of the Water Circulation System

The water circulation system consists of the intake pipe,
the settling tanks, the pumping stations, the filtering tanks,
the holding tanks, the water refrigeration system and the piping
system which circulates recycled seawater through the indoor
culture tanks (Fig. 3.3).

Seawater is pumped through an intake pipe into large
settling tanks. The end of the intake pipe submerged at sea is
surrounded by a wire cage to prevent intake of debris. The
settling tanks are used for precipitating out any mud and other
suspended debris or solids, prior to filtering.

From the settling tanks the seawater is pumped into large
scale filtering tanks which contain layers of gravel, fine sand
and activated charcoal. Seawater pumped into the top of the
filtering tanks percolates through the filters, removing colloidal
particles, fine silt and microorganisms. The purified water
is then pumped into elevated holding tanks.

Seawater is immediately pumped through inflow canals
to the upper level culture tanks in the culture room. The water
flows from higher level culture tanks to lower level culture
tanks, exiting the culture room through outflow canals. Sea
water exiting the culture room is pumped through a special
filtering tank (bypassing the settling tanks and water treament)
to be recycled through the indoor water circulation
system of the culture room. Recycled seawater is periodically
and systematically renewed by being replaced with freshly
filtered and returned seawater.

In Fujian Province the indoor gravity-fed circulation system
is sometimes supplemented with electric stirring machines that
increase water flow through the culture tanks, so that effective
cooling in the culture room is maintained in a warmer climate.

The process of seedling-rearing begins with zoospore
collection in mid-July. Zoospores are collected from parent
Laminaria stock specially selected for this purpose. To guarantee
good production of healthy zoospores, the raising of parent
Laminaria stock is often entrusted to companies which specialize
in this undertaking or is done by work units directly engaged in
seedling-rearing. The practice of specializing in the raising of
parent Laminaria stock for zoospore production has the following
advantages:

all activities relating to seedling-rearing can
be well-planned and coordinated;

robust parent stock can be separated from
general raft culture production and specially
cultured in very fertile waters using most
appropriate grow-out management techniques;

selected strains may be used for long term
interbreeding programs, creating hybrid varieties
that have desired characteristics, such as higher
production rates, higher iodine, mannitol and
alginate content and higher resistance to warm
seawater temperatures.

Selection of Sea Region for Culturing Parent Laminaria

Sea regions selected for culturing parent Laminaria stock
should have the following characteristics:

Fertile water. With dissolved nitrate and
phosphate salts in concentrations of at least 20 mg
and 5 mg per m3 respectively.

Good water exchange. Water should be clear and
moderately fast-flowing, indicating good gaseous
exchange and adequate inflow of nutrients.

Moderate transparency. Stable water transparency
not only promotes even exposure of kelp
plants to sunlight, but also prevents white rot and
green rot diseases caused by widely fluctuating
water transparency.

Lowlevelsofsiltandepiphytes. The
seawater should have low levels of suspended mud
and silt. Seawater should also be relatively free
of epiphytic seaweeds and attaching organisms which
cause frond deterioration, block photosynthesis and
inhibit development of smooth clean blades capable
of producing healthy sporangial sori.

Calculation of the Number of Parent Laminaria Required

A hatchery designed for production capacity of 400 million
young sporeling plants annually will require 8,000 to 10,000
parent Laminaria plants for spore collection. i.e. each parent
plant is calculated to produce 40,000 zoospores. In order to
guarantee sufficient quantity and quality of parent Laminaria
plants, at least twice this number should be cultivated. In
other words, 16,000 to 20,000 parent kelp plants should be grown
to achieve the given production target of 400 million young
seedlings.

Cultivation Methods

Cultivation methods used for growing parent stock differ
from normal raft culture methods. In normal kelp culture high
density planting is practiced to maximize yield at harvest. The
objective of parent Laminaria cultivation, however, is to grow
high quality plants with broad thick fronds that will develop
abundant sporangial sori.

Parent Laminaria sporelings should be selected from only the
most robust of “first batch” intermediate culture sporelings.
The young sporelings should have fronds that are wide, thick,
smooth and lustrous. They should be transplanted in low density
to short kelp culture ropes, spaced at 5 cm intervals on culture
ropes 80 cm in length, with 16 plants per culture rope. Transplantation
to culture ropes should be carried out as early as
possible in order to lengthen the grow-out season.

Kelp ropes with attached parent Laminaria should be
suspended from parallel floating raft ropes in the usual “hanging
kelp rope raft culture” method. Kelp ropes should be submerged
to a depth at which top plants on culture ropes are no deeper
than one metre below the water surface. As usual, bottom ends of
hanging culture ropes should be weighted with stones. Culture
ropes should be spaced 50 cm apart, with an overall cultivation
density of approximately 4,000 parent kelp plants per mu (60,000
per ha).

The main tasks to be performed during grow-out management of
parent Laminaria stock are: (i) adjusting the water depth of
culture ropes during different grow-out stages, (ii) reversing
hanging culture ropes to equalize illumination on all plants, and
(iii) periodic washing and cleaning of the plants to remove silt,
epiphytes and other attaching organisms.

Transplantation of parent plants to culture ropes is carried
out between mid-to-late November. For a period of time following
transplantation plants are light sensitive and so the tops of
kelp culture ropes should be submerged at a depth of 1 m to lower
illumination levels. In late February or early March the kelp
culture ropes should be reversed one time. Between late March
and early April the culture ropes should be gradually raised in
the water to a depth of 50–60 cm. Raising kelp ropes increases
illumination, thereby improving the growth and development of
broad thick fronds with good accumulation of photosynthates.
Blade tips of maturing plants may be cut during the latter half
of April to improve illumination and reduce frond deterioration.
Around mid-June the kelp ropes should be lowered to a depth of
70–80 cm in order to shade plants, since sporangial sori form
best in dim light conditions.

In general sporangial sori are first formed on the shady
side of the blade, whereas the side facing the light develops
sori more slowly. Nevertheless, maturation of sporophytes and
extent of formation of sporangial sori are closely related to
water temperature (Fig. 1.6) and light intensity. Experimental
evidence reported in Fig. 1.13 indicates that sporangial sori form
best on mature plants cultured at shallower depths of 50 and 100
cm, where light intensity is higher. Table 3.1 shows that
Laminaria fronds cultured at shallower depths mature earlier and
the proportion of plants bearing sporangial sori is higher, since
they receive higher light exposure. There is no appearance of
sporangial sori on plants cultured at lower depths even by mid-May
when seawater temperature has risen to 17.1° C, a temperature
within the range of 15–10° C is most favourable for sporangial sori
formation (Fig. 1.6).

The area of blades developing sporangial sori is also
closely related to light intensity. Fig. 3.4 shows results of a
study of sporangial sori formation on plants cultured at
different depths of 60, 100 and 200 cm. Although temperature
range and nutrient levels were optimum, results of the study
indicate that deficient illumination at lower depths results in a
decreased area of formation of sporangial sori on blades. All
measurements were made for blades of equal size. The results
again indicate that formation of sporangial sori depends on light
intensity and light duration.

Good management requires that plants should be cleaned
periodically during grow-out. This is done by shaking the kelp
ropes vigorously (without shaking plants loose) to remove settled
deposits of mud and silt. This procedure improves photosynthesis
and gaseous exchange, thus enhancing growth. Occasionally kelp
blades may need to be cleaned more thoroughly to remove any
epiphytic seaweeds or other attaching organisms clinging to the
surfaces of the fronds. This is done by lifting and hand-rubbing
individual blades, taking care not to injure blade surfaces.

Providing Fertilizer Additives

If there are insufficient levels of dissolved nutrients in
the seawater, fertilizer application is required. This is done
using either the hanging bag method (where fertilizer is placed
in plastic bags and diffuses through small pinholes into the
seawater) or the sprinkling/spraying method (where fertilizer in
low concentration solution is sprinkled by hand or sprayed with
high-pressure hoses over the seafarming area). Generally,
nitrogen-based fertilizer is applied at the rate of 150–250 kg/mu
(2,250–3,750 kg/ha) apportioned over the 6–7 month grow-out
period.

Selection of Mature Parent Laminaria

Selection of high quality parent Laminaria is done when
sporangial sori are seen forming on the fronds. Selection
should take place towards the end of June in northern China, i.e.
before the general harvest in mid-July. (Where parent plants are
selected from rafts used for general production.) Selection
should be scheduled to take place about 20 days before planned
timing of zoospore collection.

Selection Criteria

Best parent Laminaria plants are those with large areas of
sporangial sori, especially along the main mid-band of the blade.
Plants should have thick and wide blades that are pliable and
stout, with a deep lustrous colour and with a strong stipe, and
should be free of epiphytes and other clinging organisms. Blades
should have no patches of rot or deteriorating edges.

Treatment Procedures

Selected parent Laminaria plants are removed from culture
ropes and transported to shallow water. First they are trimmed
to remove parts of blade tips and edges showing signs of deterioration
or having poorly developed sporangial sori. The tangled
rhizoid is pruned, leaving only the main or primary rhizoids. The
fronds are then carefully cleaned and washed to remove attaching
organisms, epiphytes and silt.

After trimming, plants are reattached to culture ropes, 15–
20 plants being tied to each 1 m long culture rope. The culture
ropes are again suspended from rafts at a depth of 1 m in clear
seawater with moderate currents and free of silt. In this way
parent Laminaria plants are temporarily cultivated to stimulate
further maturation of sporangia and to allow recovery from the
trauma of pruning. During this temporary stocking and cultivation
period, plants should be washed periodically to prevent
accumulation of debris and silt on blades which would impede
development of sporangial sori.

Oversummering of Parent Laminaria in Southern China

In northern China, as described above, parent Laminaria
stock may be selected directly from mature plants growing on
rafts in the general production area. Selection of parent plants
is done towards the end of June. After a period of temporary
cultivation spores are collected in mid-July. The spores are
then cultured into young sporelings under artificial conditions
in seedling-rearing stations.

In southern China, for example in Fujian Province, if parent
Laminaria stock were left over the summer in the seawater they
would be severely damaged by high summer seawater temperatures.
Therefore a different procedure for cultivating parent Laminaria
stock has been adopted, called “oversummering of parent stock”
(Fig. 3.5). Oversummering prevents blade deterioration caused by
high seawater temperatures and thus conserves healthy parent
stock for use in zoospore collection in mid-September. The
“oversummering” procedure has two stages, with parent stock being
selected on two occasions:

In early June, before seawater temperature rises
above 20°C, parent stock is selected from general
raft production plants. Selected culture ropes
with chosen parent plants are moved to a temporary
location for continued growth. The location chosen
should be a place where water is clear and where
current flows are active. Here special rafts are
stationed for the purpose of temporary cultivation
of parent stock.

In early July, when seawater temperatures rise
to about 26° C in southern China (a temperature
approaching lethal levels for sporophytes), parent
stock is again selected from plants at the
temporary growing site. These plants are moved to
indoor culture tanks in a seedling station where
they are grown throughout the summer months in
artificially cooled water. The procedure is known
as “oversummering” of parent stock.

In this way parent stock is conserved, protected from exposure to
damaging effects of high summer seawater temperatures that would
be suffered without the oversummering procedure.

The Oversummering Procedure

Tips and edges of selected plants are pruned away, leaving
only a portion of mid-blade 60–70 cm long and 20 cm wide. After
washing and cleaning, the pruned parent blades are transferred to
indoor tanks in the seedling station, with 4–5 kelp plants
occupying each square metre of tank space. Here the plants are
oversummered in cooled water at 8–10° C and under controlled
illumination at 3,000–4,000 lux. One-third of the water in the
tanks should be renewed with freshly filtered seawater each day.
The cooled seawater should be recycled through a water circulation
system for at least 16 hours daily.

After 20 days of cultivation under these controlled
conditions, i.e. around mid-July, sporangial sori will begin to
form on the blades. After another 20 days, when the epidermal
layer of the sporangial sori ruptures, light intensity in the
seedling station should be reduced to 700–1,000 lux. Also, the
water temperature should be raised gradually 0.5–1.0° C every 3
days to 13° C. After 50–60 days of artificial cultivation, i.e.
towards the end of August, zoospores are ready to be collected
from mature sporangia.

Oversumering parent plants in cooled seawater delays
maturation of sporangia on parent fronds. Thus spore collecting
can be postponed up to three months. Hence the period of
seedling-rearing can be shortened by up to 80 days, resulting in
a very significant saving on production costs.

A substrate is the material on which motile zoospores settle
and attach. Laminaria spores will attach to a wide variety of
substrates, both natural and artificial, including rocks and
boulders, shells, wooden rods, bamboo poles, metal objects and
strands of rope.

Substrate materials used in seedling stations must be
lightweight and easy to handle, have large surface area and be
free of toxic substances that would affect water quality. The
two most frequently used substrates are: (i) natural palm fibre
rope and (ii) bamboo rods.

Palm Fibre Ropes

Palm fibre rope is mainly used in northern China as well as
in Fujian Province. It has high tensile strength, shows good
resistance to rotting, has a large surface area per unit length,
is easy to handle and does not exude any toxic substances. There
are many types and grades of palm rope. Palm rope aged to a dark
reddish or rust-brown colour works much better than palm rope
whose fibres are light green in colour. Freshly stripped green
fibres tend to release a sticky sap which is lethal to young
sporelings.

Palm rope should be prepared using carefully chosen palm
fibres. After removing the bark and outer skin of palm branches,
palm fibres at least 20 cm in length should be stripped and
gathered for spinning into palm rope. This is done using a
special rope-spinning machine. The final twisted strands of palm
rope substrate should be about 0.5 cm in diameter.

Bamboo Rods: Chopsticks

Floating mud and silt tend to adhere to palm fibre rope,
whereas bamboo rods, which have hard, smooth, shiny surfaces,
prevent such accumulation. Therefore bamboo rods are used as a
substrate material for zoospore collection in southern China
where muddy deposits in seawater are relatively high.

So-called “bamboo chopsticks” are slender bamboo rods that
have been split from mature bamboo poles. Each rod should be
about 35 cm long, 0.9 cm wide and 0.5 cm thick. Older bamboo at
least six years in age is best because it is harder and doesn't
exude as much fresh sap. Also older bamboo with a hollow core is
better than younger bamboo with a solid core, because the former
can be split more easily into chopsticks. During splitting it is
best to make chopsticks which are rectangular or flat in shape
with a wide shiny outer surface area.

Preparing Palm Rope for Use as a Substrate

All materials used for substrates must be thoroughly cleaned
to remove harmful organic compounds, especially tannic acid.
Procedures for processing and cleaning palm fibre rope are as
follows:

First, the newly twisted coir rope must be made pliable.
This is done by “dry hammering”, where the rope is pounded with a
special hammering machine. Each section of palm rope should be
hammered about 400 times. The process removes all remaining palm
bark and other unwanted fragments. It also makes the palm rope
very flexible and thus easy to handle.

After soaking, the palm rope should be pounded again in a
procedure called “wet hammering”, which uses the same hammering
machine as in dry hammering. Each section of rope must again be
pounded about 400 times. During hammering the rope should be
sprayed with freshwater to wash away any exuded substances.

After wet hammering the rope should be boiled in large vats
for 3–5 hours and left soaking in the water overnight. Finally
the rope is washed in clean freshwater and dried in the sun.

Preparing Bamboo Rods for Use as a Substrate

The preparation of bamboo rods is even more stringent than
preparation of palm ropes. First, the rods should be soaked in a
1% alkaline seawater solution for 30 days, changing the alkaline
seawater solution every 10 days. Then the rods should be sterilized
by boiling them in vats containing a 1% alkaline seawater
solution, with the water temperature kept above 80° C for 24
hours. After boiling, the rods should be immersed in flowing
water for 7–10 days to remove all impurities. Finally, the
bamboo rods should be spread over a clean outdoor ground area for
sun-drying.

Making Sporeling Curtains

“Sporeling curtains”, also called “culture mats”, are made
from the cleaned substrate materials and are used in seedling
stations for rearing young sporelings. They are so-named because
they look somewhat like loosely draping window curtains or woven
floor mats.

The palm rope sporeling curtain is constructed in one of two
ways, either (a) with palm ropes hanging freely between wooden or
bamboo end–pieces, or (b) with palm ropes woven inside a fixed
frame (Fig. 3.6: a,b).

Dimensions of culture mats depend on dimensions of culture
tanks used in the seedling-rearing station. The length of
culture mats should be slightly shorter than the inside width of
the culture tanks, so that the finished mats can be easily spread
inside the tanks. Mats are usually rectangular in shape, about
1.25 m in length and 0.45 m in width.

The culture mat consists of a long length of palm rope wound
between a wooden frame. Materials used for constructing the
frame must be carefully sterilized in boiling water. About 25
equally spaced small nails are fixed into each end of the frame
so that the palm fibre rope can be wound around them to form the
culture mat. For a wound culture mat 1.25 m in length and having
50 palm ropes woven end-to-end between its frame-ends, the total
length of palm rope required is: 50 × 1.25 m = 62.5 m. The coir
rope should be formed into balls and soaked in clean water to
improve its flexibility and ease of handling during the weaving
of culture mats. The end-to-end lengths of rope woven within the
culture mats are referred to as “sporeling ropes”.

After the palm rope has been wound on the frame, 5–6
additional smaller fibre cords should be woven in-and-out across
the width of the culture mat in order to strengthen the mat and
to keep the lengthwise ropes separated and evenly spaced (Fig.
3.6:3). Each completed mat can hold about 50,000 attached
sporelings.

Loose palm hairs on culture mats may cause problems since
young sporelings may easily detach from them. Therefore loose
hairs should be removed by wetting the palm rope curtains and
placing them for a short time on hot charcoal coals. This singes
and burns off any straggling hairs.

About ten bamboo chopsticks are tied tightly together, with
all shiny surfaces facing in one direction, to form a “culture
board”, 35 cm long, 9 cm wide and .5 cm thick. Pairs of bamboo
culture boards are tied back-to-back, with their shiny surfaces
facing outward. Rows of culture boards are then suspended within
a hinged wooden frame whose length fits inside the width of
culture tanks being used (Fig. 3.7). Many frames are placed
inside each culture tank. In this way a large number of culture
boards for zoospore collection can be immersed in a relatively
small volume of culture tank space. The frame holds the culture
boards at their, top and bottom ends and is hinged so that it
can support the culture boards vertically or in a slanted
position. This allows frequent adjustments to increase illumination
in the spaces between the suspended culture boards. The
method is used only in a few seedling stations in Zhejiang
Province in southern China.

Spore collection is equivalent to sowing of seeds in land
crop farming. Briefly, the process involves partial drying of
parent Laminaria fronds to stimulate release of spores from
sporangial sori. After drying stimulation the parent fronds are
placed in a small volume of seawater in the indoor culture tanks,
together with the substrate materials already described. Liberated
spores attach to the substrate materials - either palm fibre
seedling cords or bamboo chopsticks. These “seedling ropes” or
“sporeling ropes” are then placed in other culture tanks for the
duration of sporeling cultivation.

Timing of Spore Collection

Laminaria sporophytes cultured on rafts mature and release
zoospores between April and mid-July in northern China. Zospore
collection is timed to take place as late as possible, i.e. in
mid-July before summer seawater temperature rises above 20° C.
If zoospores were collected earlier, the period of cultivation in
the seedling-rearing station would have to be extended, thereby
raising production costs. A longer cultivation period would also
mean that sporeling growth would have to be inhibited, otherwise
young seedlings would have to be transplanted too early to the
grow-out rafts. Inhibiting sporeling growth would be both complex
and costly. On the other hand, if zoospore collection is delayed
too late, midsummer seawater temperature will rise above 21° C.
Above 23° C relatively few zoospores will be produced and those
that are produced will not be vigorous (Fig. 1.6).

Collecting Zoospores and Diluting Spore Density

The parent Laminaria fronds are placed
carefully in a spore collecting tank where seawater temperature
is 8–10° C. Almost immediately sporangia on the mature fronds
rupture and release spores. The fronds should be shaken
periodically to stimulate spore release. Water samples should be
checked under a microscope to observe the density and vigour of
the motile zoospores. Healthy spores swim quickly and move in
straight lines in the seawater, whereas weak spores swim slowly
and move in circles. Only strong spores should be counted. When
the spore count reaches 15–20 per field area at 100x magnificacation
under a light microscope, then spore density is optimum
for adhesion to substrate materials.

A typical standard parent Laminaria plant will have an area
of 800 cm2 of sporangial sori on its frond surface. Between 80–
100 standard parent plants are used per cubic metre of water for
collecting zoospores. The spore density in the seawater will
reach the required 15–20 spores per 100x field area within 1–1/2
to 2 hours. A good quality parent plant may be used for spore
release 2–3 times in several spore collecting tanks over a period
of 4–6 hours.

Another method is to allow spore density to exceed the
required 15–20 spores per 100x field area. This is done by
leaving parent fronds in the collecting tank for 4–6 hours. Then
the seawater containing a high density of spores can be diluted
to the required level for spore adhesion purposes. This is done
either by siphoning seawater from the spore collecting tank into
other tanks containing seawater, or by adding more seawater to
the spore collecting tank. Dilution should continue until spore
density reaches a level of 15–20 spores per 100x field area.

Spore Attachment to the Substrate Materials

Generally, 5–7 layers of palm rope culture mats are positioned
in one tank in preparation for spore attachment. After
spore adhesion takes place, the layered mats will then be
distributed to 5–7 other tanks for sporeling cultivation. (Thus
1/5th to 1/7th of the culture tanks in the seedling-rearing
station are used for the spore collecting procedure.) The
layered mats or curtains are separated with supporting blocks of
wood so that seawater can circulate between them. With the
culture mats in place, seawater containing zoospores is siphoned
into the tank, care being taken that all surface areas of the
substrate materials are well-submerged.

The density of spores attaching to the surface area of
substrate materials is critical for sporeling development. If
density is too high, development of young seedlings will be
impeded due to overcrowding and their survival rate will be
greatly reduced. The best density of spores per surface area of
substrate is about 20–50 spores per 100x field area. If spore
density is higher or lower than this range, then the rate of
sporeling growth on artificial substrates will be decreased
(Table 3.2).

Glass microscope slides are used to measure the density of
spores adhering on substrates. The slides are immersed in
seawater near the substrate materials and spores adhere to them
at the same rate that they adhere to the palm rope seedling
curtains.

The motile spores take 3–5 hours to settle and adhere to the
substrate materials when the seawater temperature is between 8–
10° C. The rate of settling and adhesion can be periodically
checked by sampling the glass slides and counting the number of
attached spores under a microscope. Spore adhesion should be
stopped as soon as the density of attached spores reaches 20–50
per 100x field area by quickly transferring the substrate
materials to other culture tanks which have been prepared with
fresh seawater.

Arrangement of palm rope seedling curtains in the culture
tanks is an important factor determining sporeling production
rates.

i. Flat Plane Arrangement

The flat plane arrangement is used mainly in Shandong and
Liaoning Provinces in northern China. Culture mats used are of
the loose-hanging type, i.e. sporeling cords freely suspended
between end-pieces rather than being woven within a fixed frame
(Fig. 3.6a). Loose-hanging sporeling curtains are easily moved
about, especially during cleaning operations (described below).

Substrate curtains are laid flat, submerged about 8–10 cm
beneath the water surface in the culture tanks. They are also
raised 8–10 cm from the bottom of the culture tanks by being held
on a supporting frame or on supporting ropes. The frame, fitted
to the sides of the culture tanks, is made of wooden or bamboo
poles spaced 2 m apart, with polyethylene ropes (diameter 0.4 cm)
tied lengthwise at 20 cm intervals between the poles (Fig. 3.8).
A simpler method is to use two ropes fixed end-to-end in the
culture tanks and raised 8 cm from the bottom of the tanks.
Culture mats are laid on top of these supporting structures,
whose purpose is to allow circulating seawater to flow freely
beneath and above them.

Fig. 3.8. Flat plane arrangement of culture mats.

a: top view showing culture mats placed in flat
position on supporting ropes in culture tank

The flat plane arrangement of culture mats has several
important advantages. Firstly, transformation from spores into
sporelings is very successful, with higher survival rates
compared to alternative methods. Secondly, all sporelings grow
evenly because they are exposed to equal light intensity.
Thirdly, this arrangement offers best advantages for efficient
operation and management of sporeling culture, with lower
manpower and production costs.

ii. Inclined Plane Arrangement

The inclined plane method of arranging culture mats is used
chiefly in Fujian Province in southern China. Culture mats are
formed of palm ropes woven within a fixed frame (Fig. 3.6b). Two
culture mats are leaned against one another, with their top edges
tied together and their lower edges spaced about 17–18 cm apart.
A stone weight is suspended from the top edges of the frames
between the two inclined culture mats to exert downward stabilizing
force. About 10–15 pairs of inclined culture mats can be
arranged in rows in each culture tank, depending on the size of
tanks being used (Fig. 3.9).

Fig. 3.9. Inclined plane arrangement of culture mats.

a: top view of culture mats in the culture tank
b: side view of pairs of inclined culture mats
arranged in a row in the culture tank

1: pairs of inclined culture mats 2: weight

The inclined mats are immersed in seawater in the culture
tanks. The depth of seawater in the tanks is therefore greater
than for the flat plane arrangement of culture mats, thus
realizing more efficient utilization of the culture tanks.

A strong disadvantage of this arrangement, however, is that
sporelings on inclined culture mats receive uneven exposure to
light, sporelings on upper parts of mats receiving more light
than those on lower parts. Consequently there is a difference in
growth rates, sporelings on upper parts of inclined culture mats
growing larger and more quickly than those on lower parts.

Sporeling culture on artificial substrates in seedling
stations is highly intensive in nature. Multiple factors
affecting production of young sporeling plants must be carefully
controlled. Some of the most important technical considerations
for high intensity production of young sporelings are the
following:

i. Water Temperature

Optimal temperature ranges for the development of male and
female gametophytes differ, the former developing best in the
range of 10–15° C, the latter in the range of 15–20° C (Tables
3.3 and 3.4).

Completion of the gametophyte generation with formation of
zygotes takes an average of 13.5 days at 10° C. Whereas at 5° C
or 15° C completion of the gametophyte generation takes an
average of 16 days (Table 3.5). Therefore water temperature in
the seedling-rearing station during the first two weeks after
zoospore collection should be maintained at a temperature of
about 10° C.

For the remaining period of sporeling growth in the seedling
station, water temperature should be maintained in the range of
8–10°C, with a maximum of 12°C.

Temperature of natural seawater near the seawater inlet to
the settling tanks should be measured daily. The temperature of
seawater entering the indoor circulation system, as well as the
indoor temperature of the culture room, should be measured
hourly. The temperature of seawater at the exit drain from the
indoor circulation system should be measured every eight hours.

ii. Light Intensity and Periodicity

Seaweeds are autotrophic, depending on good light exposure
for promoting photosynthesis. Control of light exposure includes
management of both: (a) light intensity (rate of exposure) and
(b) light periodicity (duration of exposure).

Release of zoospores can occur with or without illumination.
However under weak illumination zoospores exhibit obvious
phototaxis. Whereas under strong illumination zoospores tend to
move away from the light. The fact that embryospores germinate
either in total darkness or in light intensity varying from 50–
4,000 lux shows that light has no effect on germination of
embryospores.

During gametophyte growth optimal light intensity is around
1,000 lux. Illumination below 200 lux may result in slow growth
or may impede growth entirely (Table 3.6).

Sporelings require different light intensity in different
growing stages. From zygote formation to the time that
sporelings reach a length of 0.1 cm in length, optimum light
intensity is 1,000–2,000 lux. Between 0.5–1.0 cm, light
intensity should be increased to 2,000–3,000 lux. And sporelings
between 1–2 cm in length require relatively strong illumination
of 3,000–4,000 lux. About 10 hours of daylight is sufficient for
sporeling growth in early developmental stages (Table 3.10).

Daylight illumination changes with the weather. Fluctuations
of daylight intensity in the culture room should be
carefully monitored. Light intensity measurements should be
recorded hourly or when any noticeable weather changes occur.
The results should be compiled in a monthly summary record.
Patterns of change in daylight intensity may thus be observed,
enabling regular adjustments of illumination to desired levels.

Natural daylight intensity frequently exceeds the level of
light intensity required for optimum sporeling growth. Therefore
daylight intensity must be controlled in seedling-rearing
stations by: (a) applying white paint on the inside surfaces of
the glass roof and (b) using indoor moveable curtains installed
below the roof windows. Daylight intensity should be tested
frequently in the culture room, usually at hourly intervals.

Even distribution of illumination on sporelings can be
further controlled by rotating sporeling plants in the culture
tanks on a regular basis. This can be done during the daily
cleaning of sporeling mats.

iii. Water Quality

Measuring water quality is also part of the routine management
of sporeling production in a seedling-rearing station. This
includes taking measurements for: turbidity or transparency,
specific gravity, salinity, acidity (pH), and dissolved concentrations
of gases and elements (oxygen, carbon dioxide, nitrate-N,
ammonia-N and phosphorous). Generally, these measurements
should be taken every 3–5 days. Following rainstorms the specific
gravity and salinity of seawater entering the indoor circulation
system should be tested. Levels of dissolved ammonia-N should be
checked at least once daily so that any problems arising can be
caught quickly. Standard values for some of the main factors of
seawater quality affecting growth of Laminaria sporelings are
given in the following table:

Conditions in sporeling culture tanks differ from natural
sea conditions in several ways. Firstly, water in culture tanks
is calmer, much less agitated than natural seawater which is
buffeted by tide and wave action. Secondly, the density of
sporelings in culture tanks is greater than sporeling density on
natural substrates in seawater. For these reasons it is
important that nutrients be replenished when sporelings are
cultured intensively under artificial conditions in indoor
culture tanks.

Levels of dissolved nitrogen and phosphorous in the seawater
circulating through culture tanks have no obvious effects on
embryospore germination, but do affect growth and development of
gametophytes. Under experimental conditions, if phosphate
levels are elevated and nitrogen is removed from seawater,
gametophytes continue growing and show egg extrusion but their
rate of development is very slow (Table 3.8). In contrast, if
nitrate levels are elevated and phosphorous is removed from
seawater or lowered to concentrations below 10 mg/m3, gametophyte
development will terminate (Table 3.9). Thus good gametophyte
development requires both nitrogen and phosphorous, with
phosphorous being the critical requirement.

For the growth of young sporelings, on the other hand,
nitrogen is the critical requirement. When dissolved nitrogen
levels are reduced below 500 mg/m3 during the first 28 days after
zoospore collection, gametophytes develop very slowly and
sporeling growth is severely retarded (Table 3.9). Adequate
nutrition levels are therefore very important during the first
month of seedling-rearing in culture tanks.

Phosphorous and nitrogen-based fertilizers should be added
to the indoor culture system, the amount and rate of fertilizer
application varying at different developmental stages. Nutrients
are usually dripped into the seawater during the water-cooling
process. The following table gives recommended concentrations:

Concentrations of nutrient elements in the culture tanks
should be tested every 3–5 days and any deficiency corrected
immediately. Required amounts of fertilizer must be calculated
based on optimum concentrations for the entire volume of seawater
in the indoor circulation system.

v. Monitoring Stages of Sporeling Development

Careful daily observations of sporelings should be made
during all stages of germination, growth and development. In
their microscopic stages - as embryospores, gametophytes and
embryosporophytes - daily observations of growth should be made
under a microscope. In addition to observing the density, size
and colour of young sporelings, their tissues and cells should
also be examined to check whether sporeling plants are infected
with bacteria or other harmful organisms. Curative and/or
preventive measures should be taken as soon as diseases are
identified. When sporelings become visible to the naked eve,
observations should focus primarily on growth rate, external form
and colour of the sporelings. Again, diseases or signs of
contamination should be found as soon as possible so that
curative or preventive measures can be taken as quickly as
possible.

Before beginning the sporeling rearing season all components
of the culture room, including the piping system and the culture
tanks, should be cleaned meticulously.

Cleaning the water Supply Equipment

Settling tanks should be cleaned every 2–5 days, depending
on rate of accumulation of solids, by draining them and washing
away accumulated precipitates.

The gravel-sand-charcoal filters in the filtration tanks
should be cleaned every 7–10 days. This is done by “reverse
flushing”, where water is pumped under pressure in the direction
opposite to the normal filtration flow. The gravel-sand-charcoal
filters in the special filtration tanks that are used for
filtering recycled seawater should also be cleaned by reverse
flushing every 3–5 days. As a general rule, all tanks holding
recycled “indoor” seawater should be cleaned before cleaning the
tanks holding newly added “outdoor” seawater.

Cleaning the Sporeling Culture Room

Only designated workers should be allowed to enter the
seedling-rearing culture room. Before entering, workers should
change their footwear, putting on high rubber boots used only for
this purpose. Before entering the culture room workers should
step into a tank placed next to the entry-door containing a
solution of potassium permanganate (KMnO4). Smoking and spitting
should be prohibited in the culture room.

Special care must be taken to keep culture tanks clean.
When cleaning, culture tanks should be divided into two groups so
that substrates with attached sporelings can be moved temporarily
from one group of tanks to the other, allowing the vacant tanks
to be cleaned. Vacant tanks should then be scrubbed thoroughly
to remove weeds, fallen bits of sporelings and settled detritus.
The tanks should be well-rinsed with pressure hoses. The same
procedure is then repeated with the second group of tanks.

(b) Spray Water Pressure Method

In an adaptation of the previous method, two workers seated
at the ends of a water through hold each substrate curtain between
them. Cleaning force is applied not from manual pressure but
from water pressure created by a spray hose. A third worker,
seated between the other two workers, controls the spray hose,
moving its nozzle back and forth so that water is forced through
the mesh of the substrate material. The water pressure may be
adjusted so that less pressure is used in early stages of
sporeling development and more pressure is used in later stages.
As before, other workers in the seedling-rearing station carry
the substrate curtains from the culture tanks to the cleaning
trough and return them to the culture tanks when the spray-cleaning
is finished. Though this method of cleaning consumes
more seawater, its advantages are that speed and efficiency of
the operation are greatly improved and less manual exertion is
needed for the actual cleaning procedure.

In autumn months when the natural seawater temperature drops
below 20° C, summer sporelings should be transferred from the
seedling station to intermediate culture rafts at sea. Growing
conditions in natural seawater are much better than in the
seedling station. Therefore transfer to intermediate culture
should be undertaken as early as possible. The following
procedures are required during late stages of sporeling growth in
the seedling station in preparation for intermediate culture:

i. Increasing Light Intensity in the Culture Room

In the 3–5 day period immediately preceding transfer of
sporelings for intermediate culture, light intensity in the
culture room should be gradually increased to equal the light
intensity at the sea location.

ii. Increasing Water Flow in the Culture Tanks

In the culture room water circulates at an even rate with
few fluctuations. Current flow is relatively slow compared with
current flow caused by tides and wave action at sea. In preparation
for intermediate culture, water flow in the culture tanks
during late stages of sporeling growth should be increased.

Timing of Transfer to Intermediate Culture

Timing of intermediate culture depends on: (i) seawater
temperature and (ii) size of young sporelings in the seedling
station.

Seawater Temperature

When young sporelings are transferred to intermediate
culture before seawater temperature falls below 21° C, the rate
of development and survival of sporelings is lowered significantly,
with many sporelings becoming detached from the culture
ropes. On the other hand, intermediate culture should begin as
soon as the seawater temperature falls to 21° C, since early
intermediate culture will result in early transplantation which,
in turn, means a longer grow-out season that will result in
significantly higher output at harvest (see Chapter IV).

Size of Young Sporelings

When transfer of young sporelings is delayed they grow too
large in the culture tanks. Overcrowding of sporelings decreases
water flow in the culture tanks and lowers illumination levels.
These adverse conditions may result in weakened plants, broken
blades and increased incidence of diseases. On the other hand,
if sporeling plants are too small at time of transfer to intermediate
culture, mortality at sea is greatly increased. Optimum
size for young sporelings at time of transfer to intermediate
culture is 3–5 cm in length.

Transportation of Sporelings to the Raft Culture Site

Finally, care must be taken in transporting sporelings from
the seedling-rearing station to the sea site for intermediate
culture on raft ropes. Truck transport is used for distances of
100–300 km. When using truck transport, culture mats or other
substrates with attached sporelings should be layered in the
truck's flatbed, with sporeling plants touching between layers of
substrates. No more than 10–12 layers of substrate curtains
should be piled on one another, to avoid damage cause by
crushing. The layered culture mats should be well-wetted and, on
windy days, the load of sporelings should be covered with a
tarpaulin to prevent loss of moisture. If the journey is long,
additional seawater should be sprayed over the plants at periodic
intervals to prevent drying. Transport should usually be done at
night when the air temperature is lowest and when traffic
conditions are best.

Seedlings attached to substrate mats are loaded in similar
fashion when transport is undertaken by ship along the coast.
Alternatively, seedling mats may be immersed in large seawater
tanks. The seawater should be renewed a few times on route,
depending on the length of the journey. Sometimes blocks of ice
in plastic bags may be placed in the tanks to lower the seawater
temperature, thereby optimizing conditions during transport.